“No doubt we had, but I beg you won’t try to drag me into the matter, Mr. Holmes. What is the use of our speculating in this way when the original plans were actually found on West?”

“Well, it is certainly singular that he should run the risk of taking originals if he could safely have taken copies, which would have equally served his turn.”

“Singular, no doubt - and yet he did so.”

“Every inquiry in this case reveals something inexplicable. Now there are three papers still missing. They are, as I understand, the vital ones.”

“Yes, that is so.”

“Do you mean to say that anyone holding these three papers, and without the seven others, could construct a Bruce-Partington submarine?”

“I reported to that effect to the Admiralty. But to-day I have been over the drawings again, and I am not so sure of it. The double valves with the automatic self-adjusting slots are drawn in one of the papers which have been returned. Until the foreigners had invented that for themselves they could not make the boat. Of course they might soon get over the difficulty.”

“But the three missing drawings are the most important?”

“Undoubtedly.”

“I think, with your permission, I will now take a stroll round the premises. I do not recall any other question which I desired to ask.”

He examined the lock of the safe, the door of the room, and finally the iron shutters of the window. It was only when we were on the lawn outside that his interest was strongly excited. There was a laurel bush outside the window, and several of the branches bore signs of having been twisted or snapped. He examined them carefully with his lens, and then some dim and vague marks upon the earth beneath. Finally he asked the chief clerk to close the iron shutters, and he pointed out to me that they hardly met in the centre, and that it would be possible for anyone outside to see what was going on within the room.

“The indications are ruined by the three days’ delay. They may mean something or nothing. Well, Watson, I do not think that Woolwich can help us further. It is a small crop which we have gathered. Let us see if we can do better in London.”

Yet we added one more sheaf to our harvest before we left Woolwich Station. The clerk in the ticket office was able to say with confidence that he saw Cadogan West - whom he knew well by sight - upon the Monday night, and that he went to London by the 8:15 to London Bridge. He was alone and took a single third-class ticket. The clerk was struck at the time by his excited and nervous manner. So shaky was he that he could hardly pick up his change, and the clerk had helped him with it. A reference to the timetable showed that the 8:15 was the first train which it was possible for West to take after he had left the lady about 7:30.

“Let us reconstruct, Watson,” said Holmes after half an hour of silence. “I am not aware that in all our joint researches we have ever had a case which was more difficult to get at. Every fresh advance which we make only reveals a fresh ridge beyond. And yet we have surely made some appreciable progress.